The present invention relates generally to a dust filter apparatus of the type shown in my prior U.S. Pat. No. 4,235,610, Nov. 25, 1980, but utilizes a modified structure in which the filter elements are annular pleated fiber type filters as distinguished from the fabric bag filters employed in the above-mentioned patent. Generally speaking, apparatus of this type which employs cartridge filters find primary utility at low flow rates wherein the massive filter area and low filtering velocity combine to provide high efficiency collection of submicron particles and very economical operation.